Canonical Inflammasome Research Articles

Abstract 13544: Inflammasome Activation In Kawasaki Disease And Multisystem Inflammatory Syndrome In Children

Introduction: Multisystem Inflammatory Syndrome in Children (MIS-C) is a newly identified syndrome elicited by infection of acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although MIS-C shares several clinical features with Kawasaki disease (KD), a greater magnitude of systemic inflammation is usually associated with MIS-C. Inflammasome activation induces the secretion of pro-inflammatory cytokines, IL-1β and IL-18 and the inflammatory form of cell death, pyroptosis. To provide mechanistic insights into MIS-C and KD, we compared the expression and activation of the inflammasome in blood samples from MIS-C and KD patients. Methods: Expression levels of canonical and non-canonical inflammasome components, including NLRP3 , CASP1 , CASP4 , CASP5 , IL1B , and the inflammatory mediator, TIFA in whole blood from KD and convalescent patients were analyzed from microarray datasets. The expression of these inflammasome-related genes was further examined in whole blood samples from MIS-C, KD, KD shock syndrome (KDSS) and convalescent patients using RT-qPCR. Inflammasome activation and TIFA expression were validated in granulocytes of febrile control, KD and MIS-C patients by Western blotting. Results: TIFA , NLRP3 , CASP1 , CASP4 , CASP5 , IL1B were upregulated in whole blood from MIS-C, KD, and KDSS patients as compared to convalescent patients. However, the differences were not significant among diseases. Although gene expression profiles were similar in KD, KDSS and MIS-C whole blood RNA, the processing of canonical and non-canonical inflammasome caspases, caspase-1, and caspase-4 were only observed in granulocytes isolated from MIS-C patients, but not KD and febrile controls. Moreover, TIFA was upregulated along with the activation of the inflammasome in granulocytes of MIS-C patients. Conclusions: Our results suggest that activation of inflammasomes, especially non-canonical inflammasome induction in granulocytes, is a hallmark of MIS-C, and differentiates it from KD.

Role of the Inflammasome in Liver Disease.

The involvement of inflammasomes in the proinflammatory response observed in chronic liver diseases, such as alcohol-associated liver disease (ALD) and nonalcoholic fatty liver disease (NAFLD), is widely recognized. Although there are different types of inflammasomes, most studies to date have given attention to NLRP3 (nucleotide-binding oligomerization domain-like receptor family, pyrin domain containing 3) in the pathogenesis of ALD, NAFLD/nonalcoholic steatohepatitis, and fibrosis. Canonical inflammasomes are intracellular multiprotein complexes that are assembled after the sensing of danger signals and activate caspase-1, which matures interleukin (IL)-1β, IL-18, and IL-37 and also induces a form of cell death called pyroptosis. Noncanonical inflammasomes activate caspase-11 to induce pyroptosis. We discuss the different types of inflammasomes involved in liver diseases with a focus on (a) signals and mechanisms of inflammasome activation, (b) the role of different types of inflammasomes and their products in the pathogenesis of liver diseases, and (c) potential therapeutic strategies targeting components of the inflammasomes or cytokines produced upon inflammasome activation.

Parabens disrupt non-canonical inflammasome activation

Parabens are synthetic chemicals widely used as preservatives in cosmetics, pharmaceuticals, and foods. Although parabens, i.e., ethyl- and methyl-parabens, are considered relatively safe, study of possible health hazards has been undertaken due to the frequent exposure to parabens and their accumulation in the body. In this study, we elucidated the effect of parabens on inflammasome induction of inflammatory responses in innate immunity, such as interleukin (IL)-1β maturation and gasdermin D (GSDMD)-mediating pyroptosis. Parabens attenuated the inflammatory responses to intracellular lipopolysaccharide (LPS) triggering of non-canonical (NC) inflammasome activation, but did not alter canonical inflammasome (i.e., NLRP3, NLRC4 and AIM2) responses. The NC inflammasome is assembled by the interaction of murine caspase (Casp)-11 (Casp4/5 in human) with cytosolic LPS, inducing endotoxin sepsis. Parabens selectively inhibited NC inflammasome activation in both human and murine macrophages and diminished the peritoneal IL-1β production in LPS-injected mice. Parabens blocked the cleavage of GSDMD, Casp1, and Casp4, but did not change the expression of Casp11 or the activity of Casp1. Taken together, the results indicate that parabens could disrupt Gram-negative pathogen infection through the inhibition of NC inflammasome activation.

Caspase-11 regulates lung inflammation in response to house dust mites

Asthma is an inflammatory lung disorder characterized by mucus hypersecretion, cellular infiltration, and bronchial hyper-responsiveness. House dust mites (HDM) are the most prevalent cause of allergic sensitization. Canonical and noncanonical inflammasomes are multiprotein complexes that assemble in response to pathogen or danger-associated molecular patterns (PAMPs or DAMPs). Murine caspase-11 engages the noncanonical inflammasome. We addressed the role of caspase-11 in mediating host responses to HDM and subsequent allergic inflammation using caspase-11-/- mice, which lack caspase-11 while express caspase-1. We found that HDM induce caspase-11 expression in vitro. The presence of IL-4 and IL-13 promote caspase-11 expression. Additionally, caspase-11-/- macrophages show reduced release of IL-6, IL-12, and KC, and express lower levels of costimulatory molecules (e.g., CD40, CD86 and MHCII) in response to HDM stimulation. Notably, HDM sensitization of caspase-11-/- mice resulted in similar levels of IgE responses and hypothermia in response to nasal HDM challenge compared to WT. However, analysis of cell numbers and cytokines in bronchiolar alveolar lavage fluid (BALF) and histopathology of representative lung segments demonstrate altered inflammatory responses and reduced neutrophilia in the airways of the caspase-11-/- mice. These findings indicate that caspase-11 regulates airway inflammation in response to HDM exposure.

Tetrandrine alleviates silicosis by inhibiting canonical and non-canonical NLRP3 inflammasome activation in lung macrophages

Silicosis caused by inhalation of silica particles leads to more than ten thousand new occupational exposure-related deaths yearly. Exacerbating this issue, there are currently few drugs reported to effectively treat silicosis. Tetrandrine is the only drug approved for silicosis treatment in China, and despite more than decades of use, its efficacy and mechanisms of action remain largely unknown. Here, in this study, we established silicosis mouse models to investigate the effectiveness of tetrandrine of early and late therapeutic administration. To this end, we used multiple cardiopulmonary function test, as well as markers for inflammation and fibrosis. Moreover, using single cell RNA sequencing and transcriptomics of lung tissue and quantitative microarray analysis of serum from silicosis and control mice, our results provide a novel description of the target pathways for tetrandrine. Specifically, we found that tetrandrine attenuated silicosis by inhibiting both the canonical and non-canonical NLRP3 inflammasome pathways in lung macrophages. Taken together, our work showed that tetrandrine yielded promising results against silicosis-associated inflammation and fibrosis and further lied the groundwork for understanding its molecular targets. Our results also facilitated the wider adoption and development of tetrandirne, potentially accelerating a globally accepted therapeutic strategy for silicosis.

Inflammasome Signaling: A Novel Paradigm of Hub Platform in Innate Immunity for Cancer Immunology and Immunotherapy.

Inflammasomes are fundamental innate immune mechanisms that promote inflammation and induce an inflammatory form of programmed cell death, pyroptosis. Pyroptotic inflammasome has been reported to be closely associated with tumorigenesis and prognosis of multiple cancers. Emerging studies show that the inflammasome assembly into a higher-order supramolecular complex has been utilized to evaluate the status of the innate immune response. The inflammasomes are now regarded as cellular signaling hubs of the innate immunity that drive the production of inflammatory cytokines and consequent recruitment of immune cells to the tumor sites. Herein, we provided an overview of molecular characteristics and biological properties of canonical and non-canonical inflammasome signaling in cancer immunology and immunotherapy. We also focus on the mechanism of regulating pyroptotic inflammasome in tumor cells, as well as the potential roles of inflammasome-mediated pyroptotic cell death in cancers, to explore the potential diagnostic and therapeutic markers contributing to the prevention and treatment of cancers.

SARS-CoV-2 nucleocapsid suppresses host pyroptosis by blocking Gasdermin D cleavage.

SARS‐CoV‐2 is an emerging coronavirus that causes dysfunctions in multiple human cells and tissues. Studies have looked at the entry of SARS‐CoV‐2 into host cells mediated by the viral spike protein and human receptor ACE2. However, less is known about the cellular immune responses triggered by SARS‐CoV‐2 viral proteins. Here, we show that the nucleocapsid of SARS‐CoV‐2 inhibits host pyroptosis by blocking Gasdermin D (GSDMD) cleavage. SARS‐CoV‐2‐infected monocytes show enhanced cellular interleukin‐1β (IL‐1β) expression, but reduced IL‐1β secretion. While SARS‐CoV‐2 infection promotes activation of the NLRP3 inflammasome and caspase‐1, GSDMD cleavage and pyroptosis are inhibited in infected human monocytes. SARS‐CoV‐2 nucleocapsid protein associates with GSDMD in cells and inhibits GSDMD cleavage in vitro and in vivo. The nucleocapsid binds the GSDMD linker region and hinders GSDMD processing by caspase‐1. These insights into how SARS‐CoV‐2 antagonizes cellular inflammatory responses may open new avenues for treating COVID‐19 in the future.

Lower Temperatures Exacerbate NLRP3 Inflammasome Activation by Promoting Monosodium Urate Crystallization, Causing Gout.

Gout is a recurrent and chronic form of arthritis caused by the deposition of monosodium urate (MSU) crystals in the joints. Macrophages intake MSU crystals, the trigger for NLRP3 inflammasome activation, which leads to the release of interleukin (IL)-1β and results in the flaring of gout. The effects of temperature, an environmental factor for MSU crystallization, on IL-1β secretion have not been well studied. This study examined the effects of temperature on inflammasome activation. Specific triggers activated canonical inflammasomes (NLRP3, NLRC4, and AIM2) in murine macrophages at various temperatures (25, 33, 37, 39, and 42 °C). The maturation of IL-1β and caspase-1 was measured as an indicator for inflammasome activation. As expected, the optimal temperature of inflammasome activation was 37 °C. The MSU crystal-mediated activation of inflammasome increased at temperatures lower than 37 °C and decreased at higher temperatures. MSU crystals at lower temperatures enhanced IL-1β secretion via the NLRP3 inflammasome pathway. A lower temperature promoted the formation of MSU crystals without changing phagocytosis. Overall, lower temperatures form more MSU crystals and enhance NLRP3 inflammasome activation. In light of these findings, it is possible that hyperthermia therapy may reduce gout flaring.

Abortive HIV-1 RNA induces pro-IL-1β maturation via protein kinase PKR and inflammasome activation in humans.

The proinflammatory cytokine IL‐1β mediates high levels of immune activation observed during acute and chronic human immunodeficiency virus 1 (HIV‐1) infection. Little is known about the mechanisms that drive IL‐1β activation during HIV‐1 infection. Here, we have identified a crucial role for abortive HIV‐1 RNAs in inducing IL‐1β in humans. Abortive HIV‐1 RNAs were sensed by protein kinase RNA‐activated (PKR), which triggered activation of the canonical NLRP3 inflammasome and caspase‐1, leading to pro‐IL‐1β processing and secretion. PKR activated the inflammasome via ROS generation and MAP kinases ERK1/2, JNK, and p38. Inhibition of PKR during HIV‐1 infection blocked IL‐1β production. As abortive HIV‐1 RNAs are produced during productive infection and latency, our data strongly suggest that targeting PKR signaling might attenuate immune activation during acute and chronic HIV‐1 infection.

Mechanical Ventilation Exacerbates Poly (I:C) Induced Acute Lung Injury: Central Role for Caspase-11 and Gut-Lung Axis.

BackgroundThe mechanisms by which moderate tidal volume ventilation (MTV) exacerbates preexisting lung injury are unclear. We hypothesized that systemic endotoxemia via the gut-lung axis would lead to non-canonical and canonical inflammasome activation and pyroptosis in a two-hit model involving polyinosinic-polycytidylic acid (Poly(I:C)), a synthetic analog of dsRNA and MTV and that this would associate with acute lung injury (ALI).MethodsAnesthetized mice were administered Poly(I:C) intratracheally and then 6 h later, they were mechanically ventilated for 4 h with otherwise non-injurious MTV (10ml/kg). Changes in intestinal and alveolar capillary permeability were measured. Further documentation of ALI was assessed by evans blue albumin permeability, protein and IL-1 family concentration in bronchoalveolar lavage fluid (BALF) or plasma, and histopathology in cohorts of wildtype (WT), whole body genetically ablated caspase-11 (caspase-11-/-), caspase-1/caspase-11 double knockout (caspase-1/11-/-), gasdermin D (GSDMD)-/-, nucleotide-binding domain leucine-rich repeat-containing protein 3 (NLRP3)-/- and advanced glycosylation end product-specific receptor (RAGE) -/- mice.ResultsNon-injurious MTV exacerbated the mild lung injury associated with Poly(I:C) administration. This included the disruption of alveolar-capillary barrier and increased levels of interleukin (IL)-6, high mobility group proteins 1 (HMGB-1), IL-1β in BALF and IL-18 in plasma. Combined (Poly(I:C)-MTV) injury was associated with increase in gastrointestinal permeability and endotoxin in plasma and BALF. Poly(I:C)-MTV injury was sensitive to caspase-11 deletion with no further contribution of caspase-1 except for maturation and release of IL-18 (that itself was sensitive to deletion of NLRP3). Combined injury led to large increases in caspase-1 and caspase-11. Genetic ablation of GSDMD attenuated alveolar-capillary disruption and release of cytokines in combined injury model.ConclusionsThe previously noted exacerbation of mild Poly(I:C)-induced ALI by otherwise non-injurious MTV is associated with an increase in gut permeability resulting in systemic endotoxemia. The gut-lung axis resulted in activation of pulmonary non-canonical (cytosolic mediated caspase-11 activation) and canonical (caspase-1) inflammasome (NLRP3) mediated ALI in this two-hit model resulting in GSDMD sensitive alveolar capillary barrier disruption, pyroptosis (alveolar macrophages) and cytokine maturation and release (IL-1β; IL-18). Pharmacologic strategies aimed at disrupting communication between gut and lung, inhibition of inflammasomes or GSDMD in pyroptosis may be useful in ALI.

Luteolin prevents THP-1 macrophage pyroptosis by suppressing ROS production via Nrf2 activation

Pyroptosis plays an important role in the pathogenesis of numerous infectious, autoimmune, and inflammatory diseases, which makes it a promising target for intervention. In this study, the effect of luteolin on pyroptosis and the underlying mechanism were investigated using the canonical NLRP3 inflammasome in THP-1 macrophages induced by LPS/ATP. The results showed that luteolin exhibited a potent preventive effect on THP-1 macrophage pyroptosis, as evidenced by the increase in cell viability and the decrease in LDH release. Moreover, luteolin was found to significantly reduce the expression of NLRP3, pro-CASP-1 and CASP-1, which are the key components of NLRP3 inflammasome, as well as the expression of N-GSDMD and IL-1β, and we proved that the inhibition of luteolin on NLRP3 inflammasome activation is ROS-dependent. Furthermore, it was demonstrated that luteolin promoted Nrf2 nuclear translocation, thereby increasing the expression of HO-1 that reduces ROS production, while the anti-pyroptotic effect of luteolin was reversed by a specific Nrf2 inhibitor. Additionally, luteolin inhibited NF-κB p65 phosphorylation and nuclear translocation. In summary, we conclude that luteolin prevents THP-1 macrophage pyroptosis by suppressing ROS production via Nrf2 activation as well as NF-κB inactivation. These results support luteolin as a potential bioactive chemical against pyroptosis-related inflammatory diseases.

Canonical Inflammasome Formation in Monocytes of Sickle Cell Anemia Patients

Sickle cell anemia (SCA) is now recognized as a chronic vascular inflammatory disease, in which inflammatory mechanisms drive the vaso-occlusive process. The inflammasome complex, responsible for the maturation and release of the IL-1β and IL-18 cytokines, is formed by pattern recognition receptors (PRRs), such as the NLRP3 protein, which recognize damage (or pathogen) associated molecular patterns (DAMPs). Following recruitment of the ASC adapter protein by the PRR, caspase-1 is activated by proximity-dimerization on the inflammasome and processes pro-IL-1β and pro-IL-18 into their bioactive forms. Elevated plasma levels of IL-1β and IL-18 may play a significant role in driving SCA inflammatory processes and it is important to identify the cellular sources and molecular mechanisms that contribute to the processing of these cytokines in SCA. Elevated caspase-1 activity and IL-1β processing has previously been reported in the neutrophils of SCA individuals (Mendonça et al., ASH Abstract 2016) and we, herein, aim to determine whether inflammasome assembly also occurs in the SCA monocytes. Peripheral blood samples and monocytes, separated by percoll gradients, were obtained from healthy control individuals (CON, total N=20) and SCA patients (total N= 20, of which 10 patients were on 15-30 mg/kg/day hydroxyurea therapy). No significant differences in data obtained from patients on/off hydroxyurea therapy were observed; thus, findings from these two groups were combined. Caspase-1 activity was determined in phenotypically-characterized monocyte populations by flow cytometry (Fam-FlicaTM kit, Immunochemistry Technologies). IL-1β release was quantified by ELISA. The percentage of CD14+CD16+ inflammatory monocytes presenting caspase-1 activity was significantly augmented in SCA, when compared to CON individuals (10.6 ± 1.3, 6.5± 1.1 % caspase-1 positivity, N=20 and 13 respectively; P<0.05). Confocal immunofluorescence microscopy indicated an augmented expression of the ASC adaptor protein and ASC speck formation in unstimulated SCA monocytes (N=3), compared to CON monocytes (N=2). Accordingly, Western blotting showed a higher ASC expression in pooled SCA monocyte total cell extract (TCE, N=4), compared to that of pooled CON monocyte TCE (N=4); furthermore, increased cleaved caspase-1 (20 KDa) was identified in pooled SCA monocyte TCEs, compared to CON monocyte TCEs. Consistent with this observation, significant pro-caspase-1 co-precipitation, together with immunoprecipitated ASC, was achieved from pooled SCA monocyte lysates, while this pro-caspase-1/ASC association was almost non-detectable in CON monocyte lysates. Finally, IL-1β release by SCA monocytes (5x105 cell/ml, 37°C during 2h, N=8) was significantly abrogated by both NLRP3 inhibition (5µM MCC950) (decreased from 50.4± 14.4 to 30.3± 11.2 pg/ml released IL-1β; P<0.05) and caspase-1 inhibition (40 µM YVAD-FMK) (decreased to 20.8± 8.3 pg/ml IL-1β; P< 0.05). Interestingly, the inhibition of NFκB (10 µM BAY117082, an inhibitor of IκBα phosphorylation) also significantly reduced IL-1β release from SCA monocytes in 2h (9.64±2.66 pg/ml; N=8, P<0.01). As such, the inflammasome assembled in SCA monocytes is apparently of the NLRP3 type, and appears to involve NF-κB activated transcriptional regulation of IL-1β processing in these cells, most likely at the priming stage. Our data indicate that monocytes of SCA individuals present elevated ASC expression and oligomerization, mediated by the NLRP3 PRR sensor, culminating in augmented pro-caspase-1 recruitment by ASC and its cleavage to active caspase-1. As such, this canonical inflammasome assembly in SCA monocytes appears to contribute to the expressive quantities of IL-1β that are released by SCA monocytes; these cells may contribute to the elevated IL-1β processing that occurs in SCA, possibly representing a therapeutic target for the disease. DisclosuresConran:Bayer AG: Research Funding.

Inflammasomes in Alveolar Bone Loss.

Bone remodeling is tightly controlled by osteoclast-mediated bone resorption and osteoblast-mediated bone formation. Fine tuning of the osteoclast–osteoblast balance results in strict synchronization of bone resorption and formation, which maintains structural integrity and bone tissue homeostasis; in contrast, dysregulated bone remodeling may cause pathological osteolysis, in which inflammation plays a vital role in promoting bone destruction. The alveolar bone presents high turnover rate, complex associations with the tooth and periodontium, and susceptibility to oral pathogenic insults and mechanical stress, which enhance its complexity in host defense and bone remodeling. Alveolar bone loss is also involved in systemic bone destruction and is affected by medication or systemic pathological factors. Therefore, it is essential to investigate the osteoimmunological mechanisms involved in the dysregulation of alveolar bone remodeling. The inflammasome is a supramolecular protein complex assembled in response to pattern recognition receptors and damage-associated molecular patterns, leading to the maturation and secretion of pro-inflammatory cytokines and activation of inflammatory responses. Pyroptosis downstream of inflammasome activation also facilitates the clearance of intracellular pathogens and irritants. However, inadequate or excessive activity of the inflammasome may allow for persistent infection and infection spreading or uncontrolled destruction of the alveolar bone, as commonly observed in periodontitis, periapical periodontitis, peri-implantitis, orthodontic tooth movement, medication-related osteonecrosis of the jaw, nonsterile or sterile osteomyelitis of the jaw, and osteoporosis. In this review, we present a framework for understanding the role and mechanism of canonical and noncanonical inflammasomes in the pathogenesis and development of etiologically diverse diseases associated with alveolar bone loss. Inappropriate inflammasome activation may drive alveolar osteolysis by regulating cellular players, including osteoclasts, osteoblasts, osteocytes, periodontal ligament cells, macrophages, monocytes, neutrophils, and adaptive immune cells, such as T helper 17 cells, causing increased osteoclast activity, decreased osteoblast activity, and enhanced periodontium inflammation by creating a pro-inflammatory milieu in a context- and cell type-dependent manner. We also discuss promising therapeutic strategies targeting inappropriate inflammasome activity in the treatment of alveolar bone loss. Novel strategies for inhibiting inflammasome signaling may facilitate the development of versatile drugs that carefully balance the beneficial contributions of inflammasomes to host defense.

Great balls of fire: activation and signalling of inflammatory caspases.

Innate immune responses are tightly regulated by various pathways to control infections and maintain homeostasis. One of these pathways, the inflammasome pathway, activates a family of cysteine proteases called inflammatory caspases. They orchestrate an immune response by cleaving specific cellular substrates. Canonical inflammasomes activate caspase-1, whereas non-canonical inflammasomes activate caspase-4 and -5 in humans and caspase-11 in mice. Caspases are highly specific enzymes that select their substrates through diverse mechanisms. During inflammation, caspase activity is responsible for the secretion of inflammatory cytokines and the execution of a form of lytic and inflammatory cell death called pyroptosis. This review aims to bring together our current knowledge of the biochemical processes behind inflammatory caspase activation, substrate specificity, and substrate signalling.

Gasdermin D in peripheral nerves: the pyroptotic microenvironment inhibits nerve regeneration

Wallerian degeneration (WD) involves the recruitment of macrophages for debris clearance and nerve regeneration, and the cause of the foamy macrophages that are frequently observed in peripheral transection injuries is unknown. Recent studies indicated that these foamy cells are generated by gasdermin D (GSDMD) via membrane perforation. However, whether these foamy cells are pyroptotic macrophages and whether their cell death elicits immunogenicity in peripheral nerve regeneration (PNR) remain unknown. Therefore, we used GSDMD-deficient mice and mice with deficiencies in other canonical inflammasomes to establish a C57BL/6 J mouse model of sciatic nerve transection and microanastomosis (SNTM) and evaluate the role of GSDMD-executed pyroptosis in PNR. In our study, the GSDMD−/− mice with SNTM showed a significantly diminished number of foamy cells, better axon regeneration, and a favorable functional recovery, whereas irregular axons or gaps in the fibers were found in the wild-type (WT) mice with SNTM. Furthermore, GSDMD activation in the SNTM model was dependent on the NLRP3 inflammasome and caspase-1 activation, and GSDMD-executed pyroptosis resulted in a proinflammatory environment that polarized monocytes/macrophages toward the M1 (detrimental) but not the M2 (beneficial) phenotype. In contrast, depletion of GSDMD reversed the proinflammatory microenvironment and facilitated M2 polarization. Our results suggested that inhibition of GSDMD may be a potential treatment option to promote PNR.

RRx-001 ameliorates inflammatory diseases by acting as a potent covalent NLRP3 inhibitor.

The NLRP3 inflammasome plays a crucial role in innate immune-mediated inflammation and contributes to the pathogenesis of multiple autoinflammatory, metabolic and neurodegenerative diseases, but medications targeting the NLRP3 inflammasome are not available for clinical use. RRx-001 is a well-tolerated anticancer agent currently being investigated in phase III clinical trials, but its effects on inflammatory diseases are not known. Here, we show that RRx-001 is a highly selective and potent NLRP3 inhibitor that has strong beneficial effects on NLRP3-driven inflammatory diseases. RRx-001 inhibits the activation of the canonical, noncanonical, and alternative NLRP3 inflammasomes but not the AIM2, NLRC4 or Pyrin inflammasomes. Mechanistically, RRx-001 covalently binds to cysteine 409 of NLRP3 via its bromoacetyl group and therefore blocks the NLRP3-NEK7 interaction, which is critical for the assembly and activation of the NLRP3 inflammasome. More importantly, RRx-001 treatment attenuates the symptoms of lipopolysaccharide (LPS)-induced systemic inflammation, dextran sulfate sodium (DSS)-induced colitis and experimental autoimmune encephalomyelitis (EAE) in mice. Thus, our study identifies RRx-001 as a new potential therapeutic agent for NLRP3-driven diseases.

Pyroptosis in stroke-new insights into disease mechanisms and therapeutic strategies.

Stroke is a common disease with high mortality and disability worldwide. Different forms of cell deaths, including apoptosis and necrosis, occur in ischemic or hemorrhagic brain tissue, among which pyroptosis, a newly discovered inflammation-related programmed cell death, is generally divided into two main pathways, the canonical inflammasome pathway and the non-canonical inflammasome pathway. Caspase-mediated pyroptosis requires the assembly of inflammasomes such as NLRP3, which leads to the release of inflammatory cytokines IL-1β and IL-18 through the pores formed in the plasma membrane by GSDMD followed by neuroinflammation. Recently, pyroptosis and its relationship with inflammation have attracted more and more attention in the study of cerebral ischemia or hemorrhage. In addition, many inhibitors of pyroptosis targeting caspase, NLRP3, and the upstream pathway have been found to reduce brain tissue damage after stroke. In this review, we mainly introduce the pathology of stroke, the molecular mechanism, and process of pyroptosis, as well as the pivotal roles of pyroptosis in stroke, in order to provide new insights for the treatment of stroke.

Till cell death do us part: The protective role of inflammasome-mediated pyroptosis and genomic DNA recognition during brucellosis

Abstract Brucellosis, a zoonotic disease instigated by the bacteria Brucella, results in chronic inflammatory symptoms. Despite mechanisms utilized by Brucella for immune evasion, some pattern recognition receptors, specifically NOD-like receptors (NLRs), sense Brucella pathogen-associated molecular patterns (PAMPS) and form a multi-protein complex termed the inflammasome. The inflammasome attenuates Brucella pathogenesis through caspase-1 (canonical) or caspase-11 (non-canonical) mediated cleavage of pro-inflammatory cytokines IL-18 &amp; IL-1β. It can also activate inflammatory cell death known as pyroptosis, a mechanism rarely implicated with canonical inflammasome activation in brucellosis. Here, we evaluated in vivo canonical (Asc−/−) and non-canonical (Caspase-11−/−) inflammasome mouse models infected with Brucella abortus and determined that wildtype mice displayed increased survival and recruitment of WBCs with decreased bacteria load in comparison with Asc−/− mice. This indicates that the canonical inflammasome plays a necessary, defensive role against Brucella. Conducting in vitro B. abortus infections in Asc−/− macrophages, we further determined this protective mechanism of canonical inflammasome activation results from the activation of pyroptosis. We also found that the Brucella PAMP genomic (g)DNA instigated a high inflammatory response in wildtype macrophages that was suppressed in Asc−/− and amplified in anti-inflammatory NLR knockouts. This suggests that NLR activation occurs through sensing gDNA and may involve mechanisms of interaction among NLRs. Ultimately, these results suggest a greater importance and continued exploration of pyroptosis and the recognition of gDNA during brucellosis.

Entamoeba histolytica ‐Induced Activation of Caspase‐4 Regulates Gasdermin D Cleavage to Mediate IL‐1β Secretion in Macrophages

A hallmark of Entamoeba histolytica (Eh) invasion in the gut is acute intestinal inflammation dominated by the secretion of pro-inflammatory cytokines. Eh in contact with macrophages activates caspase-1 by the recruitment of the NLRP3 inflammasome complex in a Gal-lectin and Eh cysteine proteases 5 (EhCP-A5)-dependent manner, resulting in the maturation and secretion of interleukin (IL)-1β and IL-18. Although it is well-defined that caspase-1 activation is important in mediating the secretion of IL-1β and IL-18, the role caspase-4 play in the overall pro-inflammatory response is less identified. We have recently shown that Eh activates caspase-1/4 in macrophage that cleaved gasdermin D (GSDMD) leading to the insertion of N-terminal effector domain into the cell membrane, driving both pore formation and IL-1β secretion without causing significant cell death. In this study, we interrogated the requirements and activation mechanism for Eh-induced caspase-4 activation in cleaving GSDMD and in mediating bioactive IL-1β release. Similar to caspase-1, caspase-4 activation was dependent on Eh Gal-lectin and EhCP-A5 binding to macrophages that triggered ATP release that acted as a second signal. To determine if Eh-induced activation of caspase-4 interacted with the canonical NLRP3 inflammasome to regulate GSDMD-mediated pro-inflammatory cytokine release, CRISPR-Cas9 gene editing of caspase-1, 4, ASC, and NLRP3 THP-1 cells were utilized. Unlike caspase-1, caspase-4 activation in response to Eh was triggered within 10 min and was independent of ASC, NLRP3, and caspase-1. In the absence of caspase-1, caspase-4 activation was significantly up regulated that enhanced the cleavage of GSDMD to induce robust IL-1β secretion. Eh-induced caspase-4 played a major role in triggering GSDMD pore formation and bioactive IL-1β release as quantified by HEK-Blue™ reporter cell IL-1β assay independent of pyroptosis. This was in marked contrast to the positive control, LPS + Nigericin that induced high expression of caspase-1, enhanced GSDMD cleavage, IL-1β secretion, and massive pyroptosis. These results suggest that Eh induced “hyperactivated macrophages” led to caspase-4 dependent GSDMD cleavage and IL-1β secretion in the absence of pyroptosis important in disease pathogenesis.

Combination of dmLT and MPL-A adjuvants synergistically and differentially activates the canonical inflammasome in DCs and macrophages in the absence of pyroptosis

Abstract The initiation of innate immune responses is critical for the formation of a protective adaptive immune response following vaccination. Innate immune cells, such as dendritic cells (DCs) and macrophages, phagocytose and display antigen, produce immune modulators and migrate to lymphoid tissues, leading to the activation of naïve T cells. These professional antigen-presenting cells are activated in response to pathogen or danger associated molecular patterns, a process that is normally not robust with vaccine antigen alone. Adjuvants are able to increase the immunogenicity of vaccine antigens by influencing the activation status of these innate immune cells. Only a few vaccine adjuvants are currently approved for use in the US and, along with the discovery of novel adjuvants, combination adjuvants are likely to have a major impact on future vaccine development. Here, we investigated the ability of both the double mutant Escherichia coli heat labile toxin (dmLT) and the TLR4 agonist monophosphoryl lipid A (MPL-A) to drive innate and adaptative immune responses independently and in combination. We found that the combination adjuvant induces more robust activation of DCs and macrophages than either adjuvant alone, leading to the formation of the NLRP3 inflammasome complex and GSDMD independent secretion of IL-1b in the absence of pyroptosis. Furthermore, RNA sequencing and ingenuity pathway analysis support that the combination adjuvant may allow these DCs to polarize a multi-faceted Th1/2/17 CD4 T cell response. Because macrophages and DCs have distinct roles in the interface between innate and adaptive immunity, understanding the cellular and molecular actions of adjuvants on these cells is critical when developing new vaccines.